170 H. L. WIEMAN 



somewhat less than that of the control. The notochord was cut 

 and the section moved with the transplant. Tactile stimulation 

 in front of and behind the transplant gave no evidence of nervous 

 conduction in an anteroposterior, or reverse, direction. 



The production of a transverse ridge was not a constant feature 

 of operated embryos. The fact is mentioned because it happened 

 to be present in this particular embryo which was one of those 

 selected for sectioning. Sections show that the position of the 

 ridge does not coincide exactly with the position of the trans- 

 planted tube. The ridge was found to be due in part to the 

 growth in length and breadth of the transplant, but principally 

 to growth and differentiation of transplanted somites especially 

 toward the right side (fig. 6, B). This larger projecting end lies 

 near the original posterior end of the transplanted neural tube. 



Figure 6, C, shows a section in a sagittal plane passing through 

 the eye, otic vesicle, and the enlarged (original anterior) end of 

 the transplant. The sections begin at the animal's left side. 

 The appearance of the section shows that the transplant has not 

 only increased in size, but has undergone differentiation typical 

 of the hindbrain region from which it came. 



A section 180^ nearer to the midline (fig. 7, D) and to the 

 right shows a ^^ery broad connection between the transplant and 

 the brain in front. The section shown in E passes 100/i to the 

 right of D. The transplant is free, having no connections on 

 either side. The posterior stump is seen in this figure with three 

 thick nerve processes passing ventrally. It is separated from 

 the transplant by muscle derived from transplanted somite. 



Figure 8, F, 140/x to the right of E, passes approximately 

 through the midline, and shows the transplant free and under- 

 developed. The amount of development to be expected is 

 indicated by the appearance of the posterior stump, which is 

 large, showing every indication of differentiation. It terminates . 

 in a smooth, rounded surface. 



The section seen at G is 120^1 to the right of F and shows both 

 stumps with the transplant underdeveloped and lying free 

 between them. 



